[FFmpeg-devel] [PATCH 6/6] ffplay: use AV_PKT_FLAG_DISPOSABLE in frame drop logic

[John Stebbins]

On 11/19/2017 01:28 PM, Marton Balint wrote:
> On Sun, 19 Nov 2017, John Stebbins wrote:
>
>> ---
>> fftools/ffplay.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/fftools/ffplay.c b/fftools/ffplay.c
>> index 10a917194d..97555d5047 100644
>> --- a/fftools/ffplay.c
>> +++ b/fftools/ffplay.c
>> @@ -257,6 +257,7 @@ typedef struct VideoState {
>>     struct SwrContext *swr_ctx;
>>     int frame_drops_early;
>>     int frame_drops_late;
>> +    int drop_disposable;
>>
>>     enum ShowMode {
>>         SHOW_MODE_NONE = -1, SHOW_MODE_VIDEO = 0, SHOW_MODE_WAVES, SHOW_MODE_RDFT, SHOW_MODE_NB
>> @@ -1619,9 +1620,11 @@ retry:
>>                 duration = vp_duration(is, vp, nextvp);
>>                 if(!is->step && (framedrop>0 || (framedrop && get_master_sync_type(is) != AV_SYNC_VIDEO_MASTER)) && time > is->frame_timer + duration){
>>                     is->frame_drops_late++;
>> +                    is->drop_disposable = 1;
>>                     frame_queue_next(&is->pictq);
>>                     goto retry;
>>                 }
>> +                is->drop_disposable = 0;
>>             }
>>
>>             if (is->subtitle_st) {
>> @@ -2900,6 +2903,7 @@ static int read_thread(void *arg)
>>         infinite_buffer = 1;
>>
>>     for (;;) {
>> +        AVStream * st;
>>         if (is->abort_request)
>>             break;
>>         if (is->paused != is->last_paused) {
>> @@ -3008,6 +3012,12 @@ static int read_thread(void *arg)
>>         } else {
>>             is->eof = 0;
>>         }
>> +        st = ic->streams[pkt->stream_index];
>> +        if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
>> +            is->drop_disposable && pkt->flags & AV_PKT_FLAG_DISPOSABLE) {
>> +            av_packet_unref(pkt);
>> +            continue;
>> +        }
>>         /* check if packet is in play range specified by user, then queue, otherwise discard */
>>         stream_start_time = ic->streams[pkt->stream_index]->start_time;
>>         pkt_ts = pkt->pts == AV_NOPTS_VALUE ? pkt->dts : pkt->pts;
> I am not a fan of enabling this by default. Unknown number of packets 
> accumulate in the packet queue, unknown number of packets are processed by 
> the decoder, so we might drop packets referring to frames 1 second from 
> now... If you really want to dynamically drop packets, then at least drop 
> them right before feeding them to the decoder to get rid of the packet 
> queue latency.
>
>

The way it's coded, it can be disabled with -noframedrop.  But that would disable all frame dropping.  I can add a
separate option for this if you prefer.  And I'll move it to where packets are sent to the decoder to minimize buffering
effects.  This patch was primarily created as a means of testing that the correct frames were being marked as
disposable.  My feelings wouldn't be hurt if you asked to drop this entirely ;)

-- 
John      GnuPG fingerprint: D0EC B3DB C372 D1F1 0B01  83F0 49F1 D7B2 60D4 D0F7


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